Trucks, boats, automobiles and other vehicles are commonly equipped with various signal communication devices such as radios for receiving broadcast radio frequency (RF) signals, processing the RF signals, and broadcasting audio information to passengers. Satellite digital audio radio (SDAR) services have become increasingly popular, offering digital radio service covering large geographic areas, such as North America. Other geographic areas, such as Europe, are also beginning to offer SDAR services. These services typically receive uplinked programming which, in turn, is provided to subscriber RF receivers via satellites or terrestrial receivers. Each subscriber to the service generally possesses a digital radio having an RF receiver and one or more antennas for receiving the digital broadcast.
In satellite digital audio radio services systems, the radio RF receivers are generally configured to tune to certain frequencies, receive digital data signals at those frequencies, and decode the digital data signals, which typically include many channels of digital audio. In addition to broadcasting the encoded digital quality audio signals, the satellite service may also transmit data that may be used for various other applications. The broadcast signals may include advertising, information about warranty issues, information about the broadcast audio programs, and news, sports, and entertainment programming. Thus, the digital broadcasts may be employed for any of a number of satellite audio radio, satellite television, satellite Internet, and various other consumer services.
The broadcast signals typically take the form of multiple data streams that are transmitted at different frequencies. Each of the multiple data streams that are transmitted at different frequencies are broken into frames for transmitting data. FIG. 1 provides one example of a data stream 6 transmitted at a predetermined RF frequency in a conventional SDAR system. As shown, data stream 6 is broken up into multiple data frames 30 and burst synchronization symbols 34 that are used to provide an orderly, predictable pattern of data transmission that can be properly interpreted by receivers in the SDAR system. Each data frame 30 includes a frame synchronization symbol 32 that is transmitted at the beginning of each data frame 30 to identify to receivers the starting point of each data frame 30. Each data frame 30 is also shown including multiple data slots 36 in which transmitted data is located. As shown, each data slot 36 is identified by a slot identifier (slot 1, slot 2, . . . slot 104) that identifies the position of the specific data slot 36 relative to the frame synchronization symbol 32 in each data frame 30. Although FIG. 1 shows each frame synchronization symbol 32, burst synchronization symbol 34, and data slot 36 having bit lengths of 104, 48 and 6244, respectively, other bit lengths are possible.
In a typical system, data slots 36 are assigned to provide channels of information, such as, for example, audio channels. For example, slots 10 and 11 could be assigned to provide a music channel “A”. In this example, subscribers who wish to listen to music channel “A” would select channel “A” on their receiver. The receiver would tune to the RF frequency on which data stream 6 is transmitted, and would decode the data present in slots 10 and 11 of each data frame 30 that is received to provide audio to the subscribers. It should be appreciated that the receiver is able to identify the location of slots 10 and 11 of data stream 6 by knowing the location of the frame synchronization symbol 32, and position of slots 10 and 11 of data stream 6 relative to the frame synchronization symbol 32.
As noted above, the SDAR system is typically configured to provide multiple streams of data at various frequencies, each stream of which can contain multiple channels of information. FIG. 2 generally illustrates a typical SDAR system having multiple data streams 6, also referred to individually as STREAM 1, STREAM 2, STREAM 3 AND STREAM 4. Each of the data streams 6 is transmitted at a different RF frequency. As shown in FIG. 2, the frame synchronization symbols 32 for each of the multiple streams 6 occur at the same time. As a result, the frames 30 of each of the multiple streams 6 are aligned in time with the other multiple streams 6, as are the data slots 1-104 in each of the multiple data streams 6. Although the data frames 30 and data slots 1-104 of each of the multiple data streams 6 is aligned, it should be appreciated that the content provided in corresponding data slots of different streams 6 can be different for each stream 6. For example, slots 26-27 of STREAM 1 could be a music channel “B”, while slots 26-27 of STREAM 2 could be a “talk” channel “C.” It should be noted that because the slots of streams 6 are aligned in time, it is not possible for a subscriber to simultaneously receive the content of music channel “B” of STREAM 1 and “talk” channel “C” of STREAM 2. By providing multiple content channels in the various streams 6, the variety of content provided to subscribers is increased. Channel directory information, including information about future and current channel content, can be useful to communicate to users what is available on the various system channels.
What is needed is a method for transmitting and receiving SDAR channel directory information for multiple SDAR data streams that minimizes the system bandwidth required while reducing the amount of time needed to receive complete directory information in system receivers.